The present invention relates to an apparatus for longitudinally and transversely trimming articles moldingly formed on a plastic sheet and a process for operating such apparatus. More particularly, it relates to the apparatus and the process for trimming the articles successively molded and supplied directly from a forming machine more efficiently and suitably for automatic operation thereof together with the forming machine.
Various articles such as bath tubs and refrigerator compartments are formed by feeding a thermally softened plastic sheet continuously or a length of such sheet intermittently between a pair of opposite dies separated with each other and then engaging said dies together, which may be subjected to raised or reduced pressure as the occasion demands.
There are inevitably formed unnecessary rectangular rims surrounding the article molded according to such forming method, which must be trimmed. Various apparatuses and processes have been proposed for such trimming.
For instance, U.S. Pat. No. 4,583,436 discloses an apparatus comprising a frame means disposed at a cutting station, first knife means mounted on said frame means for movement in a longitudinal direction, first drive means operably connected to said first knife means for driving said first knife means in said longitudinal direction, said first knife means comprising a plurality of first knife-support means each supporting a first cutting knife, said first knife means further comprising adjusting means for adjusting the transverse position of said first knife-support means, second knife means mounted for movement in a transverse direction, second drive means for driving said second knife means in said transverse direction to cut said plastic sheet in said transverse direction, said second knife means comprising a plurality of second knife-support means each supporting a second cutting knife, said second knife means further comprising second adjust means for adjusting the longitudinal position of said second knife support means, and actuating means for moving said second knife means between a severing position wherein said second knives engage said plastic sheet to cut the latter in said transverse direction as said second knife means are driven by said drive means and retracted position wherein said second knives are disengaged from said plastic sheet, whereby said first and second knife means are operable to cut said plastic sheet in both longitudinal and transverse directions to thereby cut out desired portions from said plastic sheet.
Such prior art has surely overcome the defects of the older trimming apparatus, which comprises a set of upper and lower frames, each comprising four blades so arranged as to correspond to the four lines of the plastic sheet to be severed so that longitudinal and transverse trimmings are made in one shot by relatively moving said set of frame blades in vertical direction to engage with each other. Every time when a size of the molded article is varied the set of trimming frame blades had to be exchanged which necessitated many sets of blades of various sizes to be stored, which was space and time consuming. Particularly when such trimming apparatus is combined with the forming machine, which is often combined with a extruder for forming a plastic sheet to be supplied to the forming machine, during exchange of the set of blades with another set of blades, all of the trimming apparatus, the forming machine and the extruder had to be stopped.
The prior art, however, is too complex in the construction and operation thereof to efficiently and automatically operate such apparatus combined with the forming machine. This is caused mainly by using the so-called pair or clamp chains for gripping the plastic sheet at the opposite side edges to be fed to the trimming apparatus from the forming machine which necessitates a complex construction and movement of the pair of cutting members. Although the related art used the pair of cutting members consisting of an elongated support member and a tip pointed knife to be moved along the length of said oppositely arranged support member in order to cut the unnecessary rim portions to be in a one piece like a picture frame so as to efficiently recover of the waste portion in addition to the purpose of avoiding time and labour consuming exchange of the cutter blades of the further older trimming apparatus, such complex apparatus can not be combined with the forming machine of which operation speed has been considerably increased and is not suitable for automatically operating.